Cooling systems capable of removing a heat load from a heat-producing source are well known. For modest loads, a forced air system is often adequate. Forced air systems typically utilize an axial or centrifugal fan to pull or push air across the heat-producing source. For more substantial heat loads such as internal combustion engines, a liquid coolant heat exchanger or "radiator" may be used in conjunction with the fan.
The fan typically comprises a series of fan blades coupled to a spinning hub and positioned to direct ambient air flow over the radiator. The radiator comprises a plurality of tubes which are oriented generally normal to the fan axis. Each tube includes a series of fins to increase its surface area (and thus its heat transfer capacity). A liquid coolant is circulated through the heat-producing source wherein it absorbs heat energy. The coolant then passes through the radiator tubes, transferring heat energy through the tubes and fins to the ambient air flowing through the radiator. The cooled liquid is then routed back through the heat-producing source where it is once again heated. Accordingly, heat energy is continuously removed by the liquid coolant and transferred to the moving air.
Generally speaking, fan-radiator cooling systems can be classified based on the direction of air flow. In "pull" systems, the fan is positioned downstream from the radiator wherein it draws or pulls air therethrough. Pull systems are commonly found on motor vehicles such as automobiles and on some industrial cooling systems. Fan-radiator cooling systems may also be configured as "push" systems. As the name implies, push systems position the fan upstream from the radiator where the fan exhausts or pushes air through the radiator. Push-type systems are often selected based on packaging or installation limitations or where it is desirable to have cooler air passing over the fan. The present invention is directed to push-type systems and the remainder of the discussion will focus accordingly.
While push-type fan-radiator systems are effective heat exchangers, problems nevertheless remain. One problem is related to the flow characteristics of the axial fan. In particular, the output of an axial fan is not entirely axial but rather helical. The resulting flow thus has both an axial and a circumferential component. Since the circumferential flow component is not aligned with the tubes and fins of the radiator (i.e., it is not normal to the radiator surface), it contributes little to cooling. Rather, this circumferential flow increases entrance loss into the radiator, degrading overall efficiency.
Yet another problem with these systems is caused by the fan hub. Specifically, since the fan blades do not extend inwardly past the hub, the fan is unable to efficiently generate air flow into the region of the radiator that is aligned with the hub. Accordingly, a lower volumetric flow rate exists in and around the radiator center region. Stated alternatively, an inactive zone is produced in the radiator center wherein coolant flowing therethrough is unable to transfer the same amount of heat energy as coolant flowing elsewhere through the radiator. Thus, the overall heat removal capacity of the radiator is reduced. Depending on such factors as hub size, fan/radiator spacing and fan speed, the effect of the inactive zone on heat removal may be substantial.
While not known for use with fan-radiator systems, downstream guide vanes are often used with axial compressors and the like to address the problem of flow alignment. Downstream guide vanes collect air discharged by the compressor and redirect it in a generally axial direction. Unfortunately, these guide vanes do nothing to address the reduced flow through the inactive zone as discussed above.
Another means to increase volumetric flow is to increase the size of the radiator and fan or, alternatively, increase the fan speed. While these solutions improve overall heat transfer, they are disadvantageous in terms of cost, size and power requirements. In addition, they too do not address the issue of flow in the inactive zone.
Thus, there are unresolved issues with current fan-radiator cooling systems. What is needed is a push-type fan-radiator system that provides uniform, axial air flow through the radiator and, in particular, provides improved flow to the portion of the radiator located directly downstream from the fan hub. What is further needed is a system that can provide this uniform flow while minimizing pressure loss.